SolarWorld chief executive Frank Asbeck threatened to put Deutsche Solar into bankruptcy if Hemlock didn't agree to the concessions, according to the filing.

"Mr. Asbeck further threatened that SolarWorld AG would seek to re-purchase Deutsche Solar's assets out of bankruptcy for a de minimis amount and proceed with its solar panel business, thus freed of the supply agreements," Hemlock said in the complaint. "Asbeck stated that Hemlock would then have little recourse but to attempt to recover against a bankrupt and assetless debtor."

Hemlock said the contract requires Deutsche Solar to pay for the product it agreed to purchase, even though it hasn't taken delivery on it.

SolarWorld, based in Bonn, is Germany's largest maker of solar panels. Ben Santarris, a spokesman for SolarWorld's U.S. headquarters in Hillsboro, wasn't immediately available to comment.

SolarWorld has struggled in recent years to compete against cheaper solar panels imported from China, shedding hundreds of jobs in Hillsboro and across its international operations. Its stock value has plunged 96 percent over five years, and executives said in January that they had called in outside experts to review its business plan and earnings.